1. Field
Exemplary embodiments relate to three-dimensional (3D) image acquisition apparatuses and methods of generating a depth image by using the 3D image acquisition apparatuses.
2. Description of the Related Art
Research has been increasing in the fields of three-dimensional (3D) cameras or light detection and ranging (LIDAR) techniques for capturing distance information of an object. Further, one of these techniques is a time-of-flight (TOF) method which measures a traveling time of light by measuring a distance between a capturing unit and a subject (hereinafter referred to as “depth image”).
In the TOF method, light of a predetermined wavelength, e.g., near-infrared (NIR) (850 nm) is projected to a subject using a light-emitting diode (LED) or a laser diode (LD), and light of the same wavelength reflected from the subject is measured or captured using a photodiode or a camera. Thus, the TOF method may extract a depth image. Various TOF technologies have been introduced which include a series of various optical processes, such as projection of light from a light source, reflection of a subject, optical modulation, capturing, and processing.
For example, an optical shutter method is a method in which light of a predetermined wavelength (e.g., NIR 850 nm) is projected to a subject using an LED or LD, and an optical image obtained from light of the same wavelength reflected from the subject is optically modulated using an image intensifier or a predetermined solid state modulator. An image is captured using an image sensor, such as a photodiode (PD), a charge-coupled device (CCD), or complementary metal oxide semiconductor (CMOS) image sensor (CIS), included at a rear end of the image intensifier or the solid state modulator. An intensity value of the image is processed to obtain a depth image. To identify a phase difference or traveled time according to the distance of light, a high light modulation rate of about several tens to several hundreds of MHz is required. To obtain the high light modulation rate, an image intensifier may be used which includes a multi-channel plate (MCP) or a GaAs-based solid state modulator. In a related art, a GaAs-based modulator device has been released with improved characteristics and a thin-type modulator using an electro-optic material has been released.
In regard to an optical process for extracting a depth image or depth information, a method of driving a light source and a light modulator, a method of using a particular waveform, such as a triangular wave (ramp wave), and a method using a sine wave have been introduced. Methods of driving a light source and a light modulator according to respective waveforms and methods of extracting and calculating a depth image based on intensity values of captured images, i.e., various depth algorithms, have been introduced. Noise or signal distortion in a light source, a light modulator, or a capturing device (CCD or CIS) used in 3D cameras usually occurs. Therefore, the noise or signal distortion may cause an error in a depth image. To remove the noise or signal distortion, a noise component has to be removed using an appropriate device. In the related art, a method of using a higher order of a sine wave, which is a particular waveform, a method of using a code division multiple access (CDMA) method, or a method of removing random error is known to remove noise or signal distortion.
In a related art, a 3D camera using a TOF method generates one depth image by sequentially obtaining four infrared (IR) images using driving signals basically having different phases, e.g., 0, 90, 180, and 270 degrees. Motion blur is caused when capturing times of the four IR images are different from one another. In other words, as four IR images of a moving object are sequentially captured, a subject of some pixels (or images) may change, or an object of different depth information instead of the same depth information might be captured, during the whole capturing time of the four images. A frequency of motion blur is high on a boundary surface of the moving object. Further, the frequency of motion blur is also high when the object moves fast or when capturing occurs relatively slowly.
The motion blur in a depth image has different consequences in comparison to a typical motion blur. A consequence of the typical motion blur is an average image at the boundary surface of the moving object, e.g., average luminance or color with respect to other objects such as the object and the background thereof. However, instead of the average of depth images obtained for the typical motion blur, divergence is generated in calculation operations in regard to motion blur of a camera for obtaining the depth image. Thus, unexpected results are derived in regard to the motion blur of the camera. Accordingly, it is important to remove the motion blur.